title: Temperature dependence of the lipid packing in thylakoid membranes studied by time- and spectrally resolved fluorescence of Merocyanine 540.
abstract: The lipid packing of thylakoid membranes is an important factor for photosynthetic performance. However, surprisingly little is known about it and it is generally accepted that the bulk thylakoid lipids adopt the liquid-crystalline phase above -30 degrees C and that a phase transition occurs only above 45 degrees C. In order to obtain information on the nature of the lipid microenvironment and its temperature dependence, steady-state and time-resolved fluorescence measurements were performed on the fluorescence probe Merocyanine 540 (MC540) incorporated in isolated spinach thylakoids and in model lipid systems (dipalmitoyl phosphatidylcholine and dioleoyl phosphatidylethanolamine) adopting different phases. It is demonstrated that the degree and way of incorporation differs for most lipid phases--upon selective excitation at 570 nm, the amplitude of the fluorescence component that corresponds to membrane-incorporated MC540 is about 20% in gel-, 60% in rippled gel-, and 90% in liquid-crystalline and inverted hexagonal phase, respectively. For thylakoids, the data reveal hindered incorporation of MC540 (amplitude about 30% at 7 degrees C) and marked spectral heterogeneity at all temperatures. The incorporation of MC540 in thylakoids strongly depends on temperature. Remarkably, above 25 degrees C MC540 becomes almost completely extruded from the lipid environment, indicating major rearrangements in the membrane.
authors.affiliation: Wageningen University, Laboratory of Biophysics, P.O. Box 8128, 6700 ET Wageningen, The Netherlands.
authors.forename: Sashka B
authors.initials: SB
authors.lastname: Krumova
authors.forename: Rob B M
authors.initials: RB
authors.lastname: Koehorst
authors.forename: Attila
authors.initials: A
authors.lastname: Bóta
authors.forename: Tibor
authors.initials: T
authors.lastname: Páli
authors.forename: Arie
authors.initials: A
authors.lastname: van Hoek
authors.forename: Gyozo
authors.initials: G
authors.lastname: Garab
authors.forename: Herbert
authors.initials: H
authors.lastname: van Amerongen
mesh_terms: D005456:Fluorescent Dyes / Q000737:chemistry*; D008563:Membrane Lipids / Q000737:chemistry*; D015394:Molecular Structure; D011744:Pyrimidinones / Q000737:chemistry*; D013050:Spectrometry, Fluorescence; D013696:Temperature; D020524:Thylakoids / Q000378:metabolism*; D013997:Time Factors
chemical_list: D005456:Fluorescent Dyes; D008563:Membrane Lipids; D011744:Pyrimidinones; C003954:merocyanine dye